As Alexey Zakhlestins' mentions on his blog, the PHP-FPM project is now under the BSD license with the potential for it to be included in the main PHP distribution.

PHP-FPM is "deciphered" as "PHP FastCGI Process Manager" and is a patch for php to greatly improve FastCGI SAPI usage in production. It adds a bunch of additional features to php's fastcgi such as: easy php-process daemonization (with ability to specify uid/gid/chroot/log-file), safe php-processes restart (without losing requests), custom error-handling and accelerated file-upload support (requires additional support from web-server).

You can find out more about the project from its main site including a FAQ and documentation to get it up and running.